Göttingen 2025 – wissenschaftliches Programm

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P: Fachverband Plasmaphysik

P 17: Poster Session II

P 17.46: Poster

Mittwoch, 2. April 2025, 16:15–18:15, ZHG Foyer 1. OG

Comparision of absolute calibration techniques for the Thomson scattering diagnostic at W7-X — •Jannik Wagner, Golo Fuchert, Ekkehard Pasch, K. Jakob Brunner, Jens Knauer, Sergey A. Bozhenkov, Matthias Hirsch, Robert C. Wolf, and W7-X Team — Max Planck Insitute for Plasma Physics, Germany

Thomson scattering is a cornerstone diagnostic for determining plasma electron density and temperature in many nuclear fusion experiments, such as Wendelstein 7-X (W7-X). To reconstruct these parameters, absolute spectral calibration factors of the diagnostics' optical detection system are required. At W7-X, two calibrations are performed to determine these factors: A relative spectral calibration and an absolute calibration using Raman scattering of Nd:YAG laser pulses in Nitrogen. The relative calibration of the system is needed for electron temperature measurement, interpretation of the absolute calibration and extension of the latter into wavelength ranges inaccessible by Raman scattering. A recent study [1] proposes that Rayleigh scattering of laser pulses from a wavelength tunable optical parametric oscillator (OPO) in Argon could serve as a standalone-source for the absolute calibration. The calibration method has the potential to drastically reduce the systematic errors occurring from a strong dependence of the absolute calibration factors on the accuracy of the wavelength measurement in the spectral range of the Raman scattered signal. In this work, the conventional Raman calibration procedure is compared with the promising direct measurement using an OPO.

[1] E.R. Scott et al. JINST 14 C10033 (2019)

Keywords: diagnostic; optical parametric oscillator; electron density; calibration; Thomson scattering